Stimulation of the Renin-Angiotensin System (RAS) in patients with heart failure causes vasoconstriction, sodium and volume retention, norepinephrine release, and cardiac hypertrophy. Angiotensin converting enzyme (ACE) inhibitors block the formation of angiotensin II (Ang II) and suppress these deleterious effects. Despite this effective pharmacological therapy with ACE inhibitors in patients with heart failure, mortality remains high. Valsartan (CGP48933) is an orally active, potent Ang II receptor antagonist. A more specific and complete inhibition of the RAS, either at the level of the Ang II receptor alone, or in combination with ACE inhibition should provide further clinical benefit. Two Phase II studies with Valsartan in New York Heart Association Class II-IV heart failure patients showed that Valsartan produced statistically significant improvements in cardiac hemodynamics compared to placebo. In studies of hypertensives, Valsartan also has been shown to decrease blood pressure to a level similar to other antihypertensive medications, with a more favorable tolerability profile. There are two primary objectives of this placebo-controlled trial; 1) to asses the effect of Valsartan on morbidity and mortality in patients with stable, chronic NYHA Class II-IV heart failure both in patients receiving ACE inhibitors and in those patients where ACE inhibitors are contraindicated, 2) to determine the effect of Valsartan on signs and symptoms of heart failure and quality of life.